Conventional window and door manufacture has commonly used wood and metal components in forming structural members. Commonly, residential windows are manufactured from milled wood products that are assembled with glass to form typically double hung or casement units. Wood windows while structurally sound, useful and well adapted for use in many residential installations, can deteriorate under certain circumstances. Wood windows also require painting and other periodic maintenance. Wooden windows also suffer from cost problems related to the availability of suitable wood for construction. Clear wood products are slowly becoming more scarce and are becoming more expensive as demand increases. Metal components are often combined with glass and formed into single unit sliding windows. Metal windows typically suffer from substantial energy loss during winter months.
Extruded thermoplastic materials have been used in window and door manufacture. Filled and unfilled thermoplastics have been extruded into useful seals, trim, weatherstripping, coatings and other window construction components. Thermoplastic materials such as polyvinyl chloride have been combined with wood members in manufacturing PERMASHIELD.RTM. brand windows manufactured by Andersen Corporation for many years. The technology disclosed in Zanini, U.S. Pat. Nos. 2,926,729 and 3,432,883, have been utilized in the manufacturing of plastic coatings or envelopes on wooden or other structural members. Generally, the cladding or coating technology used in making PERMASHIELD.RTM. windows involves extruding a thin polyvinyl chloride coating or envelope surrounding a wooden structural member.
Recent advances have made a polyvinyl chloride/cellulosic fiber composite material useful in the manufacture of structural members for windows and doors. Puppin et al., U.S. Pat. No. 5,406,768 comprise a continuous phase of polyvinyl chloride and a particular wood fiber material having preferred fiber size and aspect ratio in a thermoplastic material that provides engineering properties for structural members and for applications in window and door manufacture. These thermoplastic composite materials have become an important part of commercial manufacture of window and door components. While these materials are sufficiently strong for most structural components used in window and door manufacture, certain components require added stiffness, tensile strength, elongation at break or other engineering property not always provided by the materials disclosed in Puppin et al.
We have examined the modification of thermoplastic materials in the continuous polymer phase, the modification of the cellulosic materials in the discontinuous cellulosic phase for improving the structural polymers of these composite materials. The prior art has recognized that certain advantages can be obtained by a judicious modification of the materials. For example, a number of additives are known for use in both thermoplastic and cellulosic materials including molding lubricants, polymer stabilizers, pigments, coatings, etc.
The prior art contains numerous suggestions regarding polymer fiber composites. Gaylord, U.S. Pat. Nos. 3,765,934, 3,869,432, 3,894,975, 3,900,685, 3,958,069 and Casper et al., U.S. Pat. No. 4,051,214 teach a bulk polymerization that occurs in situ between styrene and maleic anhydride monomer combined with wood fiber to prepare a polymer fiber composite. Segaud, U.S. Pat. No. 4,528,303 teaches a composite composition containing a polymer, a reinforcing mineral filler and a coupling agent that increases the compatibility between the filler and the polymer. The prior art also recognizes modifying the fiber component of a composite. Hamed, U.S. Pat. No. 3,943,079 teaches subjecting unregenerated cellulose fiber to a shearing force resulting in mixing minor proportions of a polymer and a lubricant material with the fiber. Such processing improves fiber separation and prevents agglomeration. The processing with the effects of the lubricant tends to enhance receptiveness of the fiber to the polymer reducing the time required for mixing. Similarly, Coran et al., U.S. Pat. No. 4,414,267 teaches a treatment of fiber with an aqueous dispersion of a vinyl chloride polymer and a plasticizer, the resulting fibers contain a coating of polyvinyl chloride and plasticizer and can be incorporated into the polymer matrix with reduced mixing energy. Beshay, U.S. Pat. Nos. 4,717,742 and 4,820,749 teach a composite material containing a cellulose having grafted silane groups. Raj et al., U.S. Pat. No. 5,120,776 teach cellulosic fibers pretreated with maleic or phthalic anhydride to improve the bonding and dispersibility of the fiber in the polymer matrix. Raj et al. teach a high density polyethylene chemical treated pulp composite. Hon, U.S. Pat. No. 5,288,772 discloses fiber reinforced thermoplastic made with a moisture pretreated cellulosic material such as discarded newspapers having a lignant content. Kokta et al., "Composites of Poly(Vinyl Chloride) and Wood Fibers. Part II. Effect of Chemical Treatment", Polymer Composites, April 1990, Volume 11, No. 2, teach a variety of cellulose treatments. The treatments include latex coating, grafting with vinyl monomers, grafting with acids or anhydrides, grafting with coupling agents such as maleic anhydride, abietic acid (See also Kokta, U.K. Application No. 2,192,397). Beshay, U.S. Pat. No. 5,153,241 teaches composite materials including a modified cellulose. The cellulose is modified with an organo titanium coupling agent which reacts with and reinforces the polymer phase. Similarly, the modification of the thermoplastic is also suggested in metal polypropylene laminates, crystallinity of polypropylene has been modified with an unsaturated carboxylic acid or derivative thereof. Such materials are known to be used in composite formation.
Maldas et al. in "Performance of Hybrid Reinforcements in PVC Composites: Part I and Part III", Journal of Testing and Evaluation, Vol. 21, No. 1, 1993, pp. 68-72 and Journal of Reinforced Plastics and Composites, Volume II, October 1992, pp. 1093-1102 teach small molecule modification of filler such as glass, mica, etc. in PVC composites. No improvement in physical properties are demonstrated as a result of sample preparation and testing. Maldas and Kokta, "Surface modification of wood fibers using maleic anhydride and isocyanate as coating components and their performance in polystyrene composites", Journal Adhesion Science Technology, 1991, pp. 1-14 show polystyrene flour composites containing a maleic anhydride modified wood flour. A number of publications including Kokta et al., "Composites of Polyvinyl Chloride-Wood Fibers. III: Effect of Silane as Coupling Agent", Journal of Vinyl Technolocy, Vol. 12, No. 3, September 1990, pp. 142-153 disclose modified polymer (other references disclosed modified fiber) in highly plasticized thermoplastic composites. Additionally, Chahyadi et al., "Wood Flour/Polypropylene Composites: Influence of Maleated Polypropylene and Process and Composition Variables on Mechanical Properties", International Journal Polymeric Materials, Volume 15, 1991, pp. 21-44 discuss polypropylene composites having polymer backbone modified with maleic anhydride.
Accordingly, a substantial need exists for an improved thermoplastic composite material that can be made of polymer and wood fiber with an optional, intentional recycle of a waste stream. A further need exists for an improved thermoplastic composite material that can be extruded into a shape that is a direct substitute for the equivalent milled shape in a wooden or metal structural member. This need requires a thermoplastic composite with creep resistance, improved heat distortion temperature having a coefficient of thermal expansion that approximates wood, a material that can be extruded into reproducible stable dimensions, a high compressive strength, a low thermal transmission rate, an improved resistance to insect attack and rot while in use and a hardness and rigidity that permits sawing, milling, and fastening retention comparable to wood members. Further, companies manufacturing window and door products have become significantly sensitive to waste streams produced in the manufacture of such products. Substantial quantities of wood waste including wood trim pieces, sawdust, wood milling by-products; recycled thermoplastic including recycled polyvinyl chloride, has caused significant expense to window manufacturers. Commonly, these materials are either burned for their heat value in electrical generation or are shipped to qualified landfills for disposal. Such waste streams are contaminated with substantial proportions of hot melt and solvent-based adhesives, waste thermoplastic such as polyvinyl chloride, paint, preservatives, and other organic materials. A substantial need exists to find a productive environmentally compatible use for such waste streams to avoid returning the materials into the environment in an environmentally harmful way. Such recycling requires that the recycled material remains largely thermoplastic. Lastly a substantial need exists to improve poly vinylchloride-cellulosic composites for use in high stress or high load bearing applications.